1. Field of the Invention
The present invention relates generally to the fields of soybean enzymes and protein chemistry. More specifically, the present invention relates to purified β1,2-xylosyltransferase and uses thereof.
2. Description of the Related Art
Immediate hypersensitivity reactions to foods occurs in 6% to 8% of children, and about 1% of adults (1), and these reactions are mediated by the production of IgE antibodies to glycoproteins in these foods (2). The majority of allergies are to foods of plant origin, and a number of allergenic proteins have been identified from peanut, wheat, barley, rye and soy (3–7). While linear amino acid sequences and conformational structures of proteins have been identified as IgE-binding epitopes (8), there is increasing evidence (9–11) that specific carbohydrate structures may also be important as allergens.
While there is some similarity in peptide sequence between the different allergenic proteins, a common characteristic is that most contain N-linked oligosaccharides having a β1,2-linked xylose attached to the β-linked mannose of the core structure (12). Furthermore, in wheat and barley glycoproteins, xylose appears to be important for allergenicity, since those proteins containing a β1,2-xylose were more reactive in vivo and in vitro than deglycosylated proteins (13). In addition, IgE from allergic patients recognized an Endo-lys C peptide containing the glycan, and this recognition was lost upon deglycosylation (14).
The enzyme that adds xylose to these N-linked glycoproteins is the plant β1,2-xylosyltransferase. The identification of this enzyme in microsomes from Phaseolus vulgaris cotyledons (15), and from sycamore cells of Acer pseudoplatanus (16) has been reported, but there are no reports on the purification or properties of the enzyme. The substrate specificity for acceptor oligosaccharide was examined with particulate enzyme preparations from these two plant sources and in both cases, the enzymes acted on acceptors having a β1,2-GlcNAc residue on the Manα1,3-arm, but GlcNAc-Man5(GlcNAc)2 was not a good acceptor. Thus, in the processing pathway, xylose may be added after the mannosidase II step (15). However, with the xylosyltransferase from the snail, Lymnaea stagnalis, the biantennary oligosaccharide containing a galactose in β1,4 linkage to the GlcNAc on the Manα1,3-arm was also an acceptor, although it was much less efficient (17). These studies suggested that xylose is added after the removal of the two mannoses on the Manα1,6-arm, but before galactoses are added to the GlcNAc residues.
The xylose units on these N-linked oligosaccharides may play a critical role in allergenicity, and may also be important in regulating the structure of the oligosaccharide chains and the targeting of these proteins. Thus, it is important to purify this enzyme in order to study its properties and specificities in the absence of interfering activities and possible inhibitors.
The prior art is deficient in the lack of a purified β1,2-xylosyltransferase. The present invention fulfills this long-standing need and desire in the art.